1. Field of the Invention
The present invention relates to a method and apparatus for detecting a location of concealed dipole transmitters and, in particular, to the precise determination of the location and orientation of such transmitters without restriction on the geometrical relationship between a receiver and the transmitter.
2. Discussion of Related Art
Underground pipes and conduits are often buried and not readily accessible. It is often necessary to locate these concealed utility conduits in order to repair and replace them. It is also important to know the location of underground utilities so that excavators can avoid them while excavating an area. Further, it is often necessary to locate the position of a drill head of a directional boring machine capable of trenchless underground drilling during a boring operation. If the location of buried utilities and/or underground drill heads are not accurately known during excavation and/or boring, substantial destruction to property, serious physical harm to a person, or even death may occur.
There are various ways to locate underground utilities and underground drill heads and therefore mitigate the harmful results discussed above, for example, using electromagnetic (EM) locators. EM locators typically include a receiver and a transmitter, which may be a radiating underground conductor. In some systems, a radiating underground conductor can be a sonde, a battery operated cylindrical device having a length of a few centimeters to few decimeters. A typical sonde has a single coil oriented along the cylindrical axis (also known as the dipole axis), with an integrated tone transmitter that causes an induced EM field to emanate symmetrically from the sonde. An aboveground EM locating receiver detects and processes the signal, and presents transmitter location information to a user. In this manner, an underground conduit pipe can be traced aboveground as a sonde is pulled or pushed through from one end, or a trenchless underground boring tool can be guided from information derived from the position of the sonde. Conventional EM locators, however, do not provide for precise determination of the location and orientation of sondes and exhibit some practical use limitations relating to the geometric relationship between the EM locator receiver and the sonde transmitter.
Therefore, there is a need for refinement of underground sonde location systems to allow for more precise determination of the location and orientation of such sondes. The more precise a locating can be, the less likely that substantial destruction to property, serious physical harm to a person, or even death may occur.